1. Field of the Invention
The present invention relates to seals for turbomachinery, and more particularly to a brush seal positioned between a rotating component and a stationary component of a turbomachine for minimizing the flow of a gas between the components.
2. Description of the Related Art
Seals between stationary and rotating parts of machinery are known in various forms. Some seals are provided for blocking the flow of a liquid or a viscous material, such as a lubricant, while other seals are directed to blocking gas flow between the stationary and rotating components.
In turbomachinery, seals are provided for preventing excessive gas flow between stationary and rotating components in order to minimize gas leakage and thereby improve the operating efficiency of the turbomachine. Among the different types of seals employed in turbomachines are labyrinth seals, O-ring seals, and brush seals, as well as others. In that regard, brush seals are often utilized in compressors and turbines of gas turbine engines and in steam turbines of power generating plants to minimize leakage gas flow between stationary and rotating components. The brush seals confine the gases within predetermined regions, such as the primary flow path for air and combustion products in a gas turbine engine, as well as cooling airflow paths within a gas turbine engine.
Brush seals generally include a plurality of metallic bristles that extend in a substantially radial direction relative to an axis of rotation. The bristles are clamped between a pair of annular backing plates that are interconnected at their radially outermost ends. The seal is stationary, with the outer ends of the bristles usually extending outwardly from between the backing plates and in a radially inward direction, toward the axis of rotation, to contact an annular surface of a rotating component, such as a compressor rotor or a turbine rotor.
Because of the sometimes relatively large gas pressure differentials that exist across brush seals, some form of support is provided at the lower pressure side of the brush seal in order to minimize pressure-induced deflection of the bristles. In that regard, bristle deflection in an axial direction of the turbomachine tends to increase the gap between the bristle ends and the rotating component, thereby reducing the effectiveness of the seal by allowing gas to flow around the inner ends of the bristles. Bristle support is usually provided on the downstream side of the seal by a radially-elongated backing plate or a separate, radially-extending surface that is parallel to and is placed against the bristles on the downstream side. In land-based or stationary turbomachines, such as steam turbines or stationary gas turbine engines, where weight is not a major consideration, sufficient rigid supporting structure can readily be provided around the portions of a brush seal to prevent axial deflection of the seal itself, as well as of the bristles. However, in applications where weight of the turbomachine is a very important consideration, such as in aircraft gas turbine engines, the heavy, rigid supporting structure that is available in land-based turbomachines is not suitable.
The present invention is directed to providing a brush seal supporting arrangement in which axial deflection of the brush seal is minimized while simultaneously minimizing the weight of the seal supporting structure.
Briefly stated, in accordance with one aspect of the present invention, there is provided a brush seal support structure for a brush seal that is positioned between a stationary turbomachine component and a rotatable turbomachine component. The purpose of the brush seal is to minimize gas flow between the components.
The structure includes an annular brush seal that has an annular upstream backing plate and an annular downstream backing plate spaced from each other and substantially parallel to each other, and a plurality of bristles that are positioned between the backing plates. The bristles are disposed substantially parallel to each other and extend outwardly from between the backing plates at an inner radial end of the brush seal toward a land surface defined by a rotating component. The backing plates are joined by a bridging member at an outer radially end of the brush seal. The downstream backing plate includes an axially-outwardly-extending lip to define an annular end face that is spaced in a downstream direction from the bristles.
A non-rotatable brush seal support is provided that includes a substantially axially-disposed brush seal contact surface that is spaced radially outwardly from the land surface. The support structure includes a radially-inwardly-facing annular groove adjacent to the annular end face of the lip. A retaining ring is carried in the annular groove and has a substantially radially-extending surface for engagement with the end face of the downstream backing plate lip.